Multidomain or Server Search from spark messanger

Team, we have installed search plugin. and we have two spark server (from different domain), For exchange server1.domain1.com and server2.domain2.com.

i can able to search the users within the same server. but i unable to search the users from one server to another server. Is there any way i can enable the same.

Note1: my both server are connected with port 5229.

Note2: we can able to add the user like userid@server2.domain2.com from server1. but can able to search the users from server1 to server2 and Viz.

Thanks

Krishna